The present invention concerns a reinforcing element for a lower region of a front bumper of a motor vehicle for the protection of pedestrians in case of the impact of a lower leg section against the lower region of the front bumper, as well as a front bumper for a motor vehicle having a first impact region which is to come into contact with a bumper bar of another motor vehicle, as well as a second lower impact region which is arranged below the first impact region and which is to come into contact with a pedestrian with his lower leg section.
In recent decades the automobile industry has to an increased extent turned to the protection of pedestrians in accidents. Reducing risks of injury in a collision between a motor vehicle and a pedestrian has gained importance considerably over the years.
For example, already decades ago in DE 30 03 568 A there was a discussion about the fact that, in an impact protection device known at the time, the pedestrian-protecting part is to be designed as a padded crossbeam which is arranged lower than the actual bumper and also in front of it. Due to this lower crossbeam, a pedestrian colliding with the vehicle should be hit so low that he is not knocked down and then run over, but tipped over the relatively soft, deformable front part of the vehicle, substantially reducing the risk of injury or at least the seriousness of the injuries. These first pedestrian-protecting parts were not successful in their time, amongst other things due to concerns of the designers as well as because of manufacturing difficulties and owing to the feared impaired aerodynamic properties and feared impaired force effects of the vehicle front.
At the end of the 90s, together with the European automobile industry there was a discussion about international regulations on pedestrian protection for vehicles. Tests were to be developed with which a motor vehicle front section can be qualitatively assessed according to the following criteria: a) impact with a lower leg, b) impact with an upper leg, c) impact with the hip, and d) impact with the head on a bonnet of a motor vehicle.
These endeavors of the European automobile industry and the legislator finally ended in directive 2003/102/EG for the protection of pedestrians and other unprotected road users before and during collisions with motor vehicles.
Some of the criteria for assessing the quality of motor vehicle front sections apply to the requirements for an impact with a lower leg. In this case at a collision speed of 40 km/h the following criteria for ACEA standard phase 1 are to be met: a) a dynamic knee bending angle between upper leg and lower leg is to be less than 21°, b) shearing in the knee or knee shearing displacement is to be less than 6 mm, and c) acceleration of the lower leg is to be less than 200 g (measured at the upper end of the tibia). Further, at a collision speed of 40 km/h the following criteria for ACEA standard phase 2 are to be met: a) a maximum dynamic knee bending angle between upper leg and lower leg of 15°, b) maximum shearing in the knee or knee shearing displacement of 6 mm, and c) maximum acceleration of the lower leg of 150 g (measured at the upper end of the tibia).
Parallel to the work on directive 2003/102/EG, different embodiments of bumper assemblies were proposed by the automobile industry for a front region of a passenger car faced with a casing. Various examples of this are to be found inter alia in EP 1 038 732 B1, in EP 1 103 428 A2, in DE 103 04 784 A1, and in EP 1 300 293 A1.
Further, from practical experience there have become known front bumpers for motor vehicles with a first impact region which is to come into contact with a bumper bar of another motor vehicle, which should also have a second impact region which is arranged below the first impact region and which is to come into contact with a pedestrian with his lower leg section. In this case the bumper is faced with an outer shell which amongst other things is to ensure a pleasant aesthetic external appearance and guarantee desired aerodynamics. Further, the bumper is supported against a cross member which is mounted by means of crash boxes or the like on the longitudinal members of the body. In this case the second, lower impact region is to have a reinforcing element which is frequently also referred to as a so-called “lower bumper stiffener” (LBS for short) for “pedestrian-protection lower leg impact”, or can be designated as a reinforcement of the lower front bumper region for the protection of pedestrians in a leg impact.
An embodiment of such a lower bumper stiffener for pedestrian-protection lower leg impact is discussed in EP 1 038 732 B1 which has already been cited above, for example. Here, the second impact region is to be arranged vertically below the first impact region, i.e. the upper and lower impact regions are to be arranged exactly one above the other, so that to the front they form a common vertical front surface. In this case the lower impact region is to be formed by the lower portion of the bumper which is mounted as a second lower cross member below the first cross member thereon by means of vertically arranged spacers. However, there are concerns as to whether with this structural design the relevant strict guidelines for reliable pedestrian protection can be met sufficiently.
Furthermore, in EP 1 038 732 B1 the reinforcing element described there is an integral part of the lower front bumper region with which it is constructed in one piece. This integral reinforcing element has a base plate with the lower side facing towards the ground, which terminates the front bumper horizontally. On this base plate are placed reinforcing ribs which extend from a front wall of the lower front bumper rearwardly in the longitudinal direction and which are arranged parallel and adjacent to each other.
However, known reinforcing elements of this kind have the considerable drawback that, due to the low height of the lower impact region above the ground, they are frequently subject to considerable mechanical impact stresses from below, e.g. when going over high curbs while parking or e.g. when entering a multi-story car park over ramps with abrupt changes of inclination of the roadway, leading to cracks. Repair of the reinforcing element which is integrally formed in the bumper in one piece requires replacement of the whole front bumper. This is associated with considerable costs. The repair costs go up further because the front bumpers are often painted in the color of the car. The necessary painting work including the corresponding work of stripping and building up lead to a loss of use for several days, which causes use of a hire car as a replacement.
Further, in DE 103 04 784 A1, which has already been discussed above, it has been proposed to design the lower impact region in the form of a so-called leg spoiler which is mounted on the bumper bar, extends downwardly and forwardly directed away from the latter, and is additionally supported by a rear, diagonally extending strut against the cross member located behind the upper impact region of the bumper with an absorber element located behind it. In this case a front edge of the leg spoiler should come to lie below the absorber element of the bumper bar, so that in an imaginary vertical section a connecting line between the upper impact region and the lower point of impingement on the leg spoiler which at best allows a vertical front surface to be expected, could arise, as is the case with EP 1 038 732 B1 which has already been cited above, because there the second impact region is located vertically below the first impact region, and which in the rather less favorable, but substantially more likely case yields an impact surface which is slightly obliquely inclined downwardly and rearwardly. However, this favors bending of the leg which has been struck, instead of ensuring that it is gently tipped up obliquely forwards.
With the leg spoiler of DE 103 04 784 A1, localized stresses upon the impact of a vehicle with a lower leg are to be reduced first and foremost. In the initial stage of an impact, the crash energy in the vicinity of the knee is to be absorbed by the damping material of the absorber element, wherein this absorber element first and foremost is to absorb the impact forces of a colliding motor vehicle and is designed accordingly. The leg spoiler then touches the lower leg at a later time at a lower point, in which case dynamic bending of the knee which cannot be avoided in this way, or initial rotation of the lower leg, will already have occurred disadvantageously. The leg spoiler is in this case to exhibit such rigidity that, as a result of the collision load, rearwardly directed bending of the leg spoiler after the fashion of a cantilever arm is caused. During bending, the leg spoiler is to absorb the collision load until maximum bending is achieved.
In this case, however, in DE 103 04 784 A1 the real progression of movement in case of a collision of a pedestrian with a motor vehicle is misjudged. There are also doubts whether with this structural design it is possible for the pedestrian who has been hit to tip over the front of the vehicle onto the bonnet, which is substantially more yielding than the road surface. Satisfactory protection of pedestrians or other unprotected road users is therefore probably not attainable.
In general, therefore, from the point of view of a responsible driver who worries about how he can protect pedestrians and other unprotected road users by passive safety installed in the car, there is an unsatisfactory situation which ultimately generates an attitude of rejection of motor vehicles with such inadequately designed front bumpers, which finally in turn makes it difficult to successfully implement suitable measures for the protection of pedestrians on a broad front.